Screw tight the lamp tail to turn on the lamp, unscrew it to turn off.
To change brightness, switch on the light first. Then switch off and fast on again until you reach the brightness that is needed. As the brightness cycles through Moonlight→High→Red→Red Flash→Green→Green Flash→SOS.
The light will not memorize the brightness level, each time it will start at Moonlight output if it is turned on again after 1 second.